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I think it goes without saying that software that is improperly or poorly written will have problems ranging from poor performance to unexpected crashes or incorrect functionality.

Python is an interpreted language, and this does present performance concerns worthy of consideration. There are numerous possibilities available for increasing the speed of Python -- PyPy and Cython to provide two examples -- and you are of course correct that in some cases it's better to write performance-critical code in a lower-level language such as C or C++, but that doesn't necessarily mean Python isn't suitable for games at all. This is precisely what I was referring to when I mentioned that you should be "able to work within the constraints presented by working with Python as a language". It's also worth noting that using an API such as PyOpenGL is offloading some of the "heavy lifting" to the GPU.

I'm not entirely sure why you randomly mentioned Lua -- which is also typically (but not always) interpreted -- but it's also an excellent choice of language for beginners; perhaps even a better choice than Python. Lua is a fast and capable scripting language with a number of great game-related libraries available.

...and yes, you're correct that professional models can look bad in unprofessional games; to look good, any given asset should be of a suitably high quality, be of an appropriate style to match other surrounding assets, and should be suitable for the technology and game it is being used in. A model created by a professional developer and intended to be used in a modern engine with specific shaders and effects will not look good without those shaders and effects.

Again, high quality appropriate assets are not the only thing necessary for a high quality game, but they're both important enough and often left out of this sort of discussion that I felt they bore special mention. As I said in my original response, engines and technology can and do have an impact, and you should consider all of these factors when deciding how to approach the look of your game.

...and again, it's important to remember we're giving advice to a beginner who will not be using the latest and greatest technologies for quite a long time if ever.

In a world where Lua exists, why would you suggest Python to a beginner for game developers?

Agreed completely, and I've just recently begun recommending Lua above Python. In this particular topic I mentioned Python first purely because it's what the OP asked about -- Lua only came up at all because of Green_Gill's completely random mentioning of it mid-post.

Realistically though, Python is still an acceptable choice for a beginner, and if Python is the language the OP is interested in it should be a perfectly fine choice for learning and for the beginning stages of development.